Generation of free radicals of quinone group-containing anti-cancer chemicals in NADPH-microsome system as evidenced by initiation of sulfite oxidation.

The prerequisit of reduction for activation of Mitomycin-C and unstability of its reduced form suggested investigation of the possible formation of free radicals (semiquinone forms) of a series of quinone-containing anticancer chemicals in vitro. The ability of rat-liver microsomes to initiate sulfite oxidation in the presence of NADPH was markedly enhanced by the addition of these chemicals. This strongly suggests that these chemicals participated in the process in the form of reactive free radicals. The reaction was specific for NADPH. Carbazilquinone was unique among others in that NADH can replace NADPH and its higher ability to initiate sulfite oxidation. Microsomes from Ehrlich ascites and AH-109A hepatoma cells were also effective, though to a lesser extent than those from rat liver on a protein basis. Generation of free radicals, though their biological significance is not clear at present, may be deemed an inherent chemical property of these chemicals.